Known video encoding methods, such as video encoding under the H.264 or more generally H.26x standard, allow for modification of compression levels locally in regions of a video frame. For example, image quality can be improved by adjusting the compression level for a region of interest (ROI) representing an object. This may also be applied to video sequences in which there are moving objects.
This is the topic of U.S. Pat. No. 8,150,173 B2 which, for example, teaches that for video sequences with moving objects, one ROI may be defined per frame. Alternatively, a starting position and size of a ROI may be specified and the specified ROI may then track the motion of the object in the video sequence.
For the purpose of reducing compression artefacts on or around the object of interest, a ROI usually includes not only the object of interest, but also a part of the background. This part of the background varies in every frame when the object is moving. As a result, the compression level used to encode a specific part of the background is varied when an object passes by, sometimes several times if the object is moving in a swaying manner. This will significantly increase the bitrate needed to encode the video sequence since the specific part of the background needs to be re-encoded with different compression levels multiple times. There is hence a need for improvements.